1. Field of the Invention
The present invention relates to a receive unit for reception of a plurality of satellite signals, and in particular to a receive unit for extracting a selected satellite signal from a plurality of satellite signals received via a plurality of low noise blocks.
2. Discussion of the Related Art
A satellite receive unit, for example the unit often referred to as an outdoor unit, comprises one or multiple LNBs (Low Noise Blocks), each arranged to amplify a satellite signal received via a parabolic satellite dish. The satellite signal for example conveys sound and/or video data, such as television signals or radio signals. Each LNB is designed to introduce as little noise as possible, which is typically in the order of 1 decibel.
The satellite signal as received by the LNB is modulated on a carrier signal, for example in a frequency band of 10.4-12.7 GHz. Within this frequency band, there are a number of channels each corresponding to a particular data stream that may comprise video and/or audio data of one or more television and/or radio broadcasts. The bandwidth of each channel is typically between 8 and 30 MHz.
Satellite receive units have been proposed that may receive signals from multiple satellites.
FIG. 1 illustrates part of a satellite system comprising satellites 102, 104, each of which is on a geostationary orbit and transmits a satellite signal. The satellite signal from each of the satellites is, for example, in the band 10.4 to 12.7 GHz. A receive unit 106 for receiving one or both satellite signals comprises for example a pair of LNBs, each aimed at a corresponding one of the satellites. One of the LNBs, for example, has a receive intensity distribution corresponding to the frontal lobe 108A and side lobes 108B and 108C, while a second LNB has a receive intensity distribution illustrated by a frontal lobe 110A and side lobes 110B and 110C.
In order for each of the LNBs to be able to correctly receive a satellite signal from a corresponding satellite, the satellites 102 and 104 are spatially separated to allow an angle of at least a between them with respect to the satellite receive unit 106. Angle α is generally in the order of 6 degrees. For example, in France, the Astra19 satellite is positioned at longitude 19° E, and the Hotbird satellite is positioned at longitude 13° E, leaving an angle of 6° longitude between the satellites such that a single satellite receiver may distinguish the signals.
Satellites for television broadcasts are generally positioned on geostationary orbits above the equator. The constraint that each satellite needs to be 6 degrees apart means that there is limited space for satellites in this region. In order to offer more services, it would be advantageous to allow more satellites to be launched in a more closely packed configuration. However, a problem is that known satellite receive units are generally not adapted to correctly receive signals from satellites closer together than 6 degrees.